1. Field of the Invention
The invention involves an impression tray for dental prosthetics, having a U-shaped running groove that has a bottom and two side walls.
2. Description of Related Art
Impression trays of this type are generally known in prophylactodontia. With them, impressions are taken of a jaw with teeth or its partial sections, for the subsequent manufacture of crowns, bridges, and other dental prostheses.
The impression trays correspond by their U-shaped contour essentially with the progression of the jaw whose impression should be taken.
Into the U-shaped running groove, a self-hardening impression paste is filled, and then an impression is made with it.
Using the impression, a positive model is then made later that functions for the dental technician""s modeling of the dental prosthesis.
The self-hardening impression paste involves especially special silicone masses, which not only represent a considerable cost factor for the impression technology, but also, in their later disposal, can be a strain on the environment, for example, because as plastics they poorly decay in landfills.
An essential problem of the customary impression pastes, however, lies in the fact that for self-hardening, some time is spent in which the impression tray usually must be held in position by an assistant in order to obtain a precise impression. If during the hardening period, the impression tray is wobbled, this can lead to an imprecise impression.
The purpose of the invention presented here is thus to further develop an impression tray as described above in such a way that a secure handling can be achieved in which wobbling that is possibly caused by the assistant can be prevented.
This purpose is achieved according to the invention in that the bottom has a thickness that is enlarging away from the ends of the legs.
Because of this special form of the bottom, the holding of the impression tray can be achieved during hardening in that the patient, on whose jaw the impression is taken, bites on the impression tray. In an impression tray with a bottom that has a constant thickness, as has been used thus far, there is the danger that the impression tray is first pressed on one end against the teeth to be molded and in this way can tilt which then leads to an imprecise impression. This is prevented by an impression tray according to the invention with a bottom that becomes thicker starting from the ends of the legs.
The invention is based on the knowledge that the lower jaw-bone (submaxilla) is moved around the mandibular joint in close approximation on a circular path. By the bottom with the thickness that is increasing from the ends of the legs, this movement is taken into account to such an extent since the bottomxe2x80x94in the side viewxe2x80x94is constructed in a circular segment shape. It is thus impinged during biting both from the upper and from the lower jaw only by forces normal to its surface. A tilting, as described above for the impression tray known thus far, can thus no longer occur.
A patient can thus achieve the necessary compression pressure himself by biting on the impression tray, without having to have an assistant hold the impression tray when the material hardens. The assistant can thus be active in other work.
In an especially advantageous embodiment, the reinforcement of the bottom is constructed at an angle of less than 5xc2x0. This angle is felt to be especially pleasant by a patient, so that when he bites on the impression tray, he can apply the necessary press-on pressure over a longer time without tension.
In another preferred embodiment form, the upper side of the bottom has a progression that rises at the ends of the leg of the U-shape.
This embodiment form is based on the knowledge that the masticatory surfaces of the teeth do not lie in a plane, but instead define a curve from the rear to the front, the so-called Spee""s curve. By the construction of the bottom according to this Spee""s curve, the application of normal forces on the impression tray can be further supported during biting.
Also, the upper side of the bottom can have a lateral slope to the inside of the U-shape. In this way, it is observed that the masticatory surfaces of left and right buccal teeth lying opposite each other on the jaw do not lie on a straight line, but on a curve, the so-called Wilson""s curve.
In an additional preferred embodiment form, the side walls of the U-shaped running groove are extended beyond the bottom and thus form a U-shaped counter-bite groove.
In this counter-bite groove, an impression paste can also be filled, so that an impression can be made simultaneously of the upper jaw (supermaxilla) and lower jaw (submaxilla). For the later modeling, it is namely advantageous to also have the counter-bite available each time.
Until now, it has been proposed in this regard to make separate impressions of the other jaw. For this purpose, the corresponding impression paste is filled into a separate impression tray, which means additional work and expense. With the shape of an impression tray proposed here now, the upper jaw and lower jaw can be molded simultaneously and the patient must be subjected to the unpleasant procedure of the impression only once. Aside from this fact, this also accelerates the work progression and takes up less time for the assistant who is occupied in making the impression.
It has also been found to be advantageous that in the bottom between the two grooves, holes going through are present. This not only leads to a secure connection between the impressions on the upper side and lower side of the impression tray, the impression paste can also hold better on the impression tray during a single impression, and thus there are no adhesives necessary or even retentions that cause a holding of the impression paste in the impression tray via a form closure. Retentions of this type are, however, difficult to clean later because of the undercuts, etc.
Instead of equipping the entire bottom of the impression tray with a thickness that is increasing away from the ends of the leg, it is also within the frame of the invention to provide the bottom of the impression tray with a bulge that runs along the U-shaped groove, which has a thickness that is increasing away from the ends of the leg. Also, with a bulge of this type, the effects can be achieved as described above.
In a preferred embodiment form of this bulge, it is constructed as a removable casting channel mold with a U-shaped progression, for the attachment of which a receptacle groove is worked into the bottom of the impression tray. In this process, it is preferable also to mold onto the impression tray, in the area of the base of the U-shaped groove, a handle that is provided with a hole that communicates with the groove, in which the casting channel mold can be inserted using a projection piece. This casting channel mold is essentially Y-shaped in this case.
In the process, the hole provided in the handle should advantageously have a cross-section that tapers conically to the groove. This conical tapering can also be done in steps.
With the impression tray, which is provided with a matching casting channel mold, there are not only the advantages as described above, that a patient applies only normal forces onto the impression tray in his mouth when he is biting, but there is also the possibility via the removable casting channel mold, for performing a multi-stage impression process: in this process, a preliminary impression can be made with the impression tray with an inserted casting channel mold, whereby the preliminary impression material is relatively coarse. After hardening of the preliminary impression material, the impression tray is taken out of the patient""s mouth again and the casting channel mold is removed. It is to be assumed that the patient already has bitten on the casting channel mold, so that by removing the casting channel mold, connection holes are made at these biting positions between the casting channel on the one hand and the hollow space formed by the tooth, etc. On the other hand, connection holes of this type are still to be made, for example, with a scalpel or a similar tool.
After the impression tray is then inserted again into the patient""s mouth, a low-viscous impression material can be introduced through the casting channel, which copies the areas to be molded in a more exact manner than the coarse preliminary impression material used at first.
In order to bring the low-viscous impression material into the casting channel, it is injected molded via the hole constructed in the handle as aforementioned. Thus, so that syringes can be connected for this purpose with the widest range of projection diameters, the hole provided for this construction is conically tapering. A syringe is pushed into the tapering hole as far as possible, whereby it then is affixed at the position that is the lowest possible for it.
The casting channel mold, which can also be used because of its cross-section that is tapering towards its ends in order to convert an impression tray according to the state of the art that has existed thus far into an impression tray with a bottom area or biting area that becomes thicker away from the ends of the impression tray, has in particular an essentially Y-shaped contour. Whereas in the process the ends, arranged in pairs as described, have a tapering cross-section as described, an additional stopper-shaped thickened area is provided on the singular cross-section. With it, the hole in the handle of the impression tray can be closed.
Furthermore, on the singular end of the Y-shaped casting channel mold, a handle loop can also be constructed. This makes it easier to pull the casting channel mold out of the casting channel in the hardened preliminary impression material. Moreover, it should also be pointed out that the casting channel mold is provided on its paired sections if necessary with tapering side struts. In this way, if necessary, a more exact guidance of low-viscous casting material can be achieved at points which lie far away from the actual main channel.
On the other hand, with side struts of this type, a fixation of the casting channel mold can also be achieved in the U-shaped groove of a traditional impression tray, before the casting channel mold is held there by casting material filled in the impression tray.
The respective conical construction of the casting channel not only has the advantage that the casting channel mold is easier to remove, but also, that low-viscous casting material injected into the casting channel is distributed uniformly.